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Re: Allosauris weirdilis



In a message dated 96-02-23 11:56:21 EST, jpoling@infinet.com (Jeff Poling)
writes:

>   While flipping through my Carnegie Museum book for info on the Morrison
>Formation, the picture of their Allosaurus caught my eye.
>
>   The first thoratic? rib seems to be literally bent behind and around the
>shoulder girdle.  A quick perusal of my meager references failed to turn up
>another dinosaur with such an arangement.

Thoracic rib...

Watch out for the Carnegie dinosaurs. Lots of them are mounted incorrectly.
I've been to the Carnegie twice now, most recently for the 1995 SVP meeting,
and I've seen what I think you're referring to in the skeleton. As I recall,
the scapula is incorrectly stuck beneath the rib whereas it should have been
mounted above/upon it. One or two of the posterior cervical ribs may be
mounted atop the scapulocoracoids, too.

The Carnegie _Stegosaurus_ is mounted with a single vertical row of tail
spikes and prepubic processes that extend _outside_ the last thoracic ribs.

Etc.

>   1)  Is this actually how things would have been aranged in life, or is it
>the mistake of the preparator?

Mistake of preparator, it seems to me.

>   2)  Assuming it is correct, why?  What advantages does it give?
>   3)  Assuming it is correct, why do no other dinosaurs show this
>arangement?

Not correct; that's why no other dinosaurs show this arrangement(!).

>   And while I'm at it, Dinogeorge posted once that he thought the
>Allosaurs' first rib was really a furcula.  Looking at the picture, the ribs
>in question above have the general shape I might expect a furcula to have,
>but they aren't fused at the ends.  None of the other nearby ribs seem like
>a good candidate to be this furcula.

That's the first _abdominal_ rib--part of the basket of ribs that
protects/holds in the underbelly--not the first thoracic rib.

>   Am I remembering George correctly?  If it isn't the mystery ribs above,
>which ribs might be the furcula?  Does the Carnegie mount have the
>misdiagnosed furcula?

No furcula in the mount. Best photos of probable _Allosaurus_ furculae are on
p. 38 of Madsen's _Allosaurus_ monograph (1976; reprinted 1993), where they
are identified as abdominal ribs of an unidentified theropod from the
Cleveland-Lloyd Quarry.